The present invention relates to an internal combustion engine.
Japanese Laid-Open Patent Publication No. 2002-256966 describes an example of a cylinder head of an internal combustion engine having multiple cylinders. The cylinder head includes a pair of intake ports and a pair of exhaust ports for each cylinder. The cylinder head includes an inter-port coolant passage between the paired exhaust ports. Coolant flows through the inside of the cylinder block and then into the inter-port coolant passage. The inter-port coolant passage is configured such that the coolant flows from an outer side toward an inner side in a radial direction with respect to the central axis of the cylinder. That is, the inter-port coolant passage includes a radial outer end. The radial outer end functions as an inlet part that allows the coolant to flow from the cylinder block into the inter-port coolant passage. Arrangement of such an inter-port coolant passage in the cylinder head may improve the cooling efficiency of a combustion chamber of the internal combustion engine.
If the amount of coolant flowing through the inter-port coolant passage is increased, the cooling efficiency of the combustion chamber may be enhanced. However, the inter-port coolant passage is arranged between paired exhaust ports, and thus it is difficult to increase the cross-sectional area of the inter-port coolant passage because of limitations imposed on the layout of the inter-port coolant passage. It is thus desirable to increase the flow rate of coolant in the inter-port coolant passage for the purpose of further enhancing the cooling efficiency of the combustion chamber.